Methods to protect selective catalyst reducer aftertreatment devices during uncontrolled diesel particulate filter regeneration

ABSTRACT

The present invention is directed to a method to operate an electronically controlled internal combustion engine with an exhaust system equipped with a diesel particulate filter upstream of a selective catalyst reducer to protect the selective catalyst reducer from premature aging and failure caused by exhaust temperature heat generated during uncontrolled regeneration of the diesel particulate filter.

TECHNICAL FIELD

On diesel engines requiring both NOx and particulate aftertreatmentsystems, it is likely that some systems will use both urea selectivecatalytic reducers (SCR) in combination with diesel particulate filters(DPF). In systems where the DPF is located upstream of a urea SCRcatalyst, any uncontrolled regenerations or other high temperatureexcursions in the DPF could also put the SCR at risk of premature agingand failure. In systems where the DPF is upstream of the SCR, this isespecially a factor. There is a need to protect the SCR during periodsof uncontrolled DPF regeneration to ensure SCR long service life andprevent premature aging and failure caused by exposure to high heat.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a method tooperate an electronically controlled internal combustion engine equippedwith a Engine Control System (ECS) and an exhaust system with a DieselParticulate Filter (DPF) having an inlet and an outlet, the DPF locatedupstream of a Selective Catalytic Reducer (SCR) having an inlet and anoutlet and at least one temperature sensor electronically connected tothe ECS to transmit data signals to the ECS indicative of thetemperature at the SCR inlet. The SCR is in fluid connection with a ureasource. The method is directed to protecting the SCR during uncontrolledDPF regeneration. The method comprises the steps of:

determining engine operating mode;

determining whether the DPF is regenerating;

sensing whether the DPF outlet temperature or SCR inlet temperatureexceeds a predetermined threshold for a predetermined period of time;

introducing urea to said SCR in an amount sufficient to minimizeover-temperature to the SCR during DPF regeneration below saidpredetermined temperature threshold. In one embodiment, urea isintroduced to the SCR by an injector in fluid communication with a ureasource. The injector is responsive to commands from said ECS.

The method may further include a clean up catalyst to catalyze anyexcess ammonia slip that may be produced by the introduction of urea tocool the SCR. The method may further include the use of a dump valveresponsive to commands from the ECS to reroute some or all of theexhaust gas in said exhaust system to bypass said SCR duringuncontrolled DPF regeneration. The dump valve is controlled by the ESCand actuated responsive to the introduction of urea. If, after theintroduction of urea, the SCR inlet temperature continues to exceed apredetermined threshold for a predetermined period of time the ESCactuates the dump valve to divert the flow of exhaust gas from the SCR,thereby cooling the SCR. The diverted exhaust gas may be vented to theatmosphere or diverted around the SCR and from there, out of the exhaustsystem.

While the method is effective at all modes of engine operation,preferably, enhanced SCR inlet temperature cooling results may be seenwhen the engine operating mode is engine idle.

In another embodiment, the present invention is directed to a method tooperate an electronically controlled internal combustion engine equippedwith an Engine Control System (ECS), an exhaust system equipped with aDiesel Particulate Filter (DPF) having an inlet and an outlet. At leastone temperature sensor is position proximal to the SCR inlet and iselectronically connected to the ECS to transmit data signals indicativeof the temperature at the SCR inlet. The DPF is positioned upstream of aSelective Catalytic Reducer having an inlet and an outlet, and theexhaust system is further provided with a protector to preventoverheating of the SCR during uncontrolled DPF regeneration. The methodcomprises the steps of:

determining engine operating mode:

determining whether the DPF is regenerating;

sensing whether the DPF outlet temperature or SCR inlet temperatureexceeds a predetermined threshold for a predetermined period of time;

actuating the protector to prevent overheating of the SCR duringuncontrolled DPF regeneration.

In one embodiment, the protector may be comprised of a source of ureaand an injector in fluid communication with said urea and said SCR tofacilitate the introduction of an amount of urea in sufficient quantityover a sufficient period of time to cool the SCR inlet below apredetermined temperature for a predetermined period of time duringuncontrolled DPF regeneration. A clean up catalyst is used to catalyzeany excess ammonia slip from the introduction of urea to the SCR duringDPF regeneration.

In another embodiment, the protector may be a dump valve actuated bysaid ECS to divert some or all of the exhaust gas from the SCR duringuncontrolled DPF regeneration. The dump valve is responsive to commandsfrom the ECS to divert exhaust from the SCR when the SCR inlettemperature exceeds a predetermined temperature for a predeterminedperiod of time during uncontrolled DPF regeneration.

Whereas the methods of the present invention are useful and operationalat all modes of engine operation, enhanced results are seen when theengine is operating at engine idle mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an engine system showing thevarious systems and components, including an exhaust system with a DPFupstream of an SCR.

FIG. 2 is a software flow chart of one embodiment according to thepresent invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Turning now to the drawings wherein like numbers refer to likestructures, vehicle system 10 includes internal combustion engine 12having cylinders 14 disposed within block 16 for reciprocal movementtherein. The engine may be of any construction, such as a spark ignitionengine or a compression ignition engine, and is preferably a compressionignition type engine. The engine is electronically controlled by anEngine Control System 18 (ECS) that may be comprised of a single moduleor multiple modules, as is well known in the art. The ECS has memory,such as PROM, EPROM, EEPROM, FLASH, volatile and nonvolatile memory, andmay also have tables or maps therein within which are loaded operatinginstructions and other information necessary for the operation andcontrol of the engine and any system. In a preferred embodiment, theEngine Control System has DDEC operating instructions and programsloaded therein such as is available from Detroit Diesel Corporation. TheECS communicates and controls the engine through the enginecommunication area network (ECAN) 20 that permits the ECS to receivesensor input from the engine and to send commands from the ECS tocontrol operation of the engine.

The engine has an exhaust system 22 comprised of an exhaust conduit 24in fluid communication with an exhaust 21 of the engine to vent exhaustgasses 62 out of exhaust exit 60 that are produced in the combustionchambers of the engine to the ambient atmosphere after it is treated forremoval of Particulate Matter (PM), and NOx. The exhaust system ispreferably equipped with a Diesel Particulate Filter (DPF) 26 to removePM from the exhaust gasses. The DPF has an inlet 28 and an outlet 30. Inclose proximity to the DPF outlet, a pressure sensor 32 is disposed tosend data signals indicative of DPF inlet pressure to the ECS. The ECSdetermines if the DPF inlet pressure is indicative of a clogged DPFfilter, at which time, it initiates a regeneration of the DPF bycontrolling fueling, timing, BOT, engine mode of operation, engine loadand engine speed, etc., of the engine to create the requisite heat inthe exhaust stream to burn the PM and other hydrocarbon contaminatesfrom the DPF filter. Generally, the DPF is upstream from a SelectiveCatalyst Reducer 42. The SCR has an inlet 44 and an outlet 50. At leastone temperature sensor 46 is disposed proximal to said SCR inlet and isin electronic communication 48 with the ECS to transmit data signals tothe ECS indicative of the temperature of the exhaust gasses at the SCRinlet. Disposed in conduit 24 intermediate to the DPF and the SCR is adump or diverter valve 36 that is actuated by the ECS over electroniccommunication 38 in response to temperature readings received from thetemperature sensor 46. Valve 36 may be actuated to divert the flow ofexhaust gasses around the SCR when it is determined that the temperatureat the SCR inlet exceeds a predetermined threshold for a predeterminedperiod of time. In one embodiment, when the exhaust temperature exceedsthat threshold of temperature and time, the ECS actuates the valve todivert the flow of exhaust gas through diverter conduit 40 around theSCR and exits the exhaust gas to the ambient atmosphere through exhaustexit 60. The exhaust system may further be equipped with a urea injector56 that is electronically controlled by the ECS responsive to thetemperature at the SCR inlet. When the temperature inlet temperatureexceeds a predetermined threshold for a predetermined period of time,the ECS causes the urea injector to inject urea from urea source 52through urea conduit 54 to the SCR inlet in an attempt to cool the SCRtemperature. The amount of urea to be injected during the methods of thepresent invention is dependent upon the temperature at the SCR inlet,and is in an amount sufficient to cool the SCR inlet temperature below apredetermined threshold for predetermined period of time. In order toaccommodate the injection of urea into the exhaust stream, a catalyticcleaner 64 may be utilized in the exhaust conduit downstream of the SCRto effectively neutralize any ammonia slip caused by the introduction ofexcessive urea into the SCR during DPF regeneration events.

FIG. 2 is a software flowchart showing one embodiment of one method 66of the present invention. Specifically, step 68 is determining theengine mode of operation. Step 70 is determining whether the DPF isregenerating. Generally, DPF regeneration occurs during idle engineoperation as well as during on highway engine operation. A runaway DPFregeneration event usually occurs during a drop to idle engine mode ofoperation, and is of particular concern as such an event generates agreat amount of heat in the exhaust gas stream. The excessive exhaustheat, especially that generated during a runaway DPF regeneration eventmay harm the SCR or, in the very least, may contribute to prematureaging and failure of the SCR. Step 72 is sensing the temperature at theSCR inlet. If the temperate at the SCR inlet exceeds a predeterminedtemperature for a predetermined period of time, step 74 is actuating aprotector to control the temperature of the SCR. In one embodiment, thisstep includes injecting urea in an amount sufficient to cool the SCRbelow the predetermined temperature threshold for a predetermined periodof time. In the event the injection of urea does not cool the SCRsufficiently, a protector such as the diverter valve may be actuated todivert the flow of hot exhaust gas from the SCR. In another embodiment,the dump valve is actuated to divert the flow off exhaust gas throughthe exhaust conduit around the SCR to help cool the SCR.

The words used in the specification are understood to be words ofdescription, and not words of limitation. Many variations andmodifications are possible without departing form the scope and spiritof the invention as set forth in the appended claims.

1. A method to operate an electronically controlled internal combustionengine equipped with a Engine Control System (ECS) and an exhaust systemwith a Diesel Particulate Filter (DPF) having an inlet and an outlet,said DPF upstream of a Selective Catalytic Reducer (SCR) having an inletand an outlets and at least one temperature sensor at said SCR inlet orDPF outlet electronically connected to said ECS to transmit data signalsto said ECS indicative of temperature at said SCR inlet, said SCR influid connection with a urea source; said method to protect the SCRduring uncontrolled DPF regeneration comprising: determining engineoperating mode; determining whether the DPF is regenerating; sensingwhether the SCR inlet temperature exceeds a predetermined threshold fora predetermined period of time: introducing urea to said SCR in anamount sufficient to cool the SCR during DPF regeneration below saidpredetermined temperature threshold.
 2. The method of claim 1, furtherincluding a clean up catalyst to catalyze any excess ammonia slip. 3.The method of claim 1, further including a dump valve responsive tocommands from said ECS to reroute exhaust gas in said exhaust system tobypass said SCR during uncontrolled DPF regeneration.
 4. The method ofclaim 3 wherein said dump valve is controlled by said ESC and actuatedresponsive to the introduction of urea if said SCR inlet temperaturecontinues to exceed a predetermined threshold for a predetermined periodof time.
 5. The method of claim 1, wherein said engine operating mode isengine idle.
 6. The method of claim 1, wherein said urea is introducedto said SCR by an injector in fluid communication with a urea source;said injector responsive to commands from said ECS.
 7. A method tooperate an electronically controlled internal combustion engine equippedwith an Engine Control System (ECS), an exhaust system equipped with aDiesel Particulate Filter (DPF) having an inlet and an outlet, said DPFpositioned upstream of a Selective Catalytic Reducer having an inlet andan outlet, at least one temperature sensor at said SCR inletelectronically connected to said ECS to transmit data signals to saidECS indicative of temperature at said SCR inlet, and a protector toprevent overheating of the SCR during uncontrolled DPF regeneration,comprising: determining engine operating mode: determining whether theDPF is regenerating; sensing whether the SCR inlet temperature exceeds apredetermined threshold for a predetermined period of time; actuatingsaid protector to prevent overheating of said SCR during uncontrolledDPF regeneration.
 8. The method of claim 7, wherein said protector iscomprised of a source of urea and an injector in fluid communicationwith said urea and said SCR to facilitate the introduction of an amountof urea in sufficient quantity over a sufficient period of time to coolthe SCR inlet below a predetermined temperature for a predeterminedperiod of time during uncontrolled DPF regeneration.
 9. The method ofclaim 8, further including a clean tip catalyst to catalyze any excessammonia slip.
 10. The method of claim 7, wherein said protector is adump valve actuated by said ECS to divert exhaust gas from said SCRduring uncontrolled DPF regeneration; said dump valve responsive tocommands from said ESC to divert exhaust from said SCR when said SCRinlet temperature exceeds a predetermined temperature for apredetermined period of time during uncontrolled DPF regeneration. 11.The method of claim 7, wherein the engine operating mode is engine idle.12. The method of claim 10, wherein said dump valve vents said exhaustfrom said exhaust system.